Gene Center Munich, Department of Biochemistry, University of Munich, Munich, Germany.
Department of Chemistry, SYNMIKRO Research Center, Philipps-University Marburg, Marburg, Germany.
EMBO J. 2021 Feb 1;40(3):e105643. doi: 10.15252/embj.2020105643. Epub 2020 Dec 11.
In eukaryotes, most secretory and membrane proteins are targeted by an N-terminal signal sequence to the endoplasmic reticulum, where the trimeric Sec61 complex serves as protein-conducting channel (PCC). In the post-translational mode, fully synthesized proteins are recognized by a specialized channel additionally containing the Sec62, Sec63, Sec71, and Sec72 subunits. Recent structures of this Sec complex in the idle state revealed the overall architecture in a pre-opened state. Here, we present a cryo-EM structure of the yeast Sec complex bound to a substrate, and a crystal structure of the Sec62 cytosolic domain. The signal sequence is inserted into the lateral gate of Sec61α similar to previous structures, yet, with the gate adopting an even more open conformation. The signal sequence is flanked by two Sec62 transmembrane helices, the cytoplasmic N-terminal domain of Sec62 is more rigidly positioned, and the plug domain is relocated. We crystallized the Sec62 domain and mapped its interaction with the C-terminus of Sec63. Together, we obtained a near-complete and integrated model of the active Sec complex.
在真核生物中，大多数分泌蛋白和膜蛋白都被 N 端信号序列靶向内质网，其中三聚体 Sec61 复合物充当蛋白导通道 (PCC)。在翻译后模式下，完全合成的蛋白质被含有 Sec62、Sec63、Sec71 和 Sec72 亚基的专用通道识别。最近该 Sec 复合物在空闲状态下的结构揭示了预打开状态的整体架构。在这里，我们展示了酵母 Sec 复合物与底物结合的冷冻电镜结构，以及 Sec62 胞质结构域的晶体结构。信号序列类似于先前的结构插入 Sec61α 的侧门，但门采用更开放的构象。信号序列两侧是两个 Sec62 跨膜螺旋，Sec62 的胞质 N 端结构域的位置更刚性，而插塞结构域则重新定位。我们对 Sec62 结构域进行了结晶，并绘制了它与 Sec63 C 端的相互作用图。结合起来，我们获得了活性 Sec 复合物的近乎完整和集成模型。
